Abstract：The response mechanism of animals against environment pressure may be different between sexes. Relative fatness is a convenient index always used to indicate survive quality. Rainfall, temperature and normalized difference vegetation index (NDVI) are normally considered as environmental forecast factors. In order to understand the characteristic of relative fatness of Microtus fortis population and the relationship between relative fatness and environmental forecast factors, a population survey at 7 survey sites was implemented in Dongting Lake wetland. The habitat type was different for all the survey sites. At the same time, the data of rainfall, temperature and NDVI were collected during the study period. The correlation between the relative fatness and environmental forecast factors were analysed. The results showed that the characteristics between different sexes of M. fortis were similar. There were significant differences between the relative fatness of male and female M. fortis in different habitats during spring and winter, while variety trends of relative fatness of male and female M. fortis were similar in summer and autumn. In the wetland region, the relative fatness of male and female M. fortis was similar between seasons in carex habitat, but the difference was found in reed habitat. There was no obvious correlation between the relative fatness of male M. fortis and environmental forecast factors, irrespective of the rainfall, temperature, and NDVI in wetland or NDVI in farmland. Statistics analysis showed that the relative fatness of female M. fortis had a relationship with rainfall and NDVI in farmland, but no correlation with temperature and NDVI in wetland. The relative fatness of M. fortis may reflect the ecological pressure in some cases. Above results showed that the female M. fortis are more sensitive to environment factors than the males. Habitat and food available may affect the relative fatness of the female M. fortis and then explain the population increasing.